This is a note to let you know that I've just added the patch titled
kswapd: assign new_order and new_classzone_idx after wakeup in sleeping
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kswapd-assign-new_order-and-new_classzone_idx-after-wakeup-in-sleeping.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From f0dfcde099453aa4c0dc42473828d15a6d492936 Mon Sep 17 00:00:00 2001
From: Alex Shi <[email protected]>
Date: Mon, 31 Oct 2011 17:08:45 -0700
Subject: kswapd: assign new_order and new_classzone_idx after wakeup in sleeping
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From: Alex Shi <[email protected]>
commit f0dfcde099453aa4c0dc42473828d15a6d492936 upstream.
Stable note: Fixes https://bugzilla.redhat.com/show_bug.cgi?id=712019. This
patch reduces kswapd CPU usage.
There 2 places to read pgdat in kswapd. One is return from a successful
balance, another is waked up from kswapd sleeping. The new_order and
new_classzone_idx represent the balance input order and classzone_idx.
But current new_order and new_classzone_idx are not assigned after
kswapd_try_to_sleep(), that will cause a bug in the following scenario.
1: after a successful balance, kswapd goes to sleep, and new_order = 0;
new_classzone_idx = __MAX_NR_ZONES - 1;
2: kswapd waked up with order = 3 and classzone_idx = ZONE_NORMAL
3: in the balance_pgdat() running, a new balance wakeup happened with
order = 5, and classzone_idx = ZONE_NORMAL
4: the first wakeup(order = 3) finished successufly, return order = 3
but, the new_order is still 0, so, this balancing will be treated as a
failed balance. And then the second tighter balancing will be missed.
So, to avoid the above problem, the new_order and new_classzone_idx need
to be assigned for later successful comparison.
Signed-off-by: Alex Shi <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Reviewed-by: Minchan Kim <[email protected]>
Tested-by: Pádraig Brady <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
mm/vmscan.c | 2 ++
1 file changed, 2 insertions(+)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2908,6 +2908,8 @@ static int kswapd(void *p)
balanced_classzone_idx);
order = pgdat->kswapd_max_order;
classzone_idx = pgdat->classzone_idx;
+ new_order = order;
+ new_classzone_idx = classzone_idx;
pgdat->kswapd_max_order = 0;
pgdat->classzone_idx = pgdat->nr_zones - 1;
}
Patches currently in stable-queue which might be from [email protected] are
queue-3.0/kswapd-avoid-unnecessary-rebalance-after-an-unsuccessful-balancing.patch
queue-3.0/kswapd-assign-new_order-and-new_classzone_idx-after-wakeup-in-sleeping.patch
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